1. Field of the Invention
The present invention relates generally to the packaging of integrated circuits. More particularly, the present invention relates to a method and apparatus for providing high density chips on a printed circuit board or other substrate using leadless leadframe packages.
2. Description of the Related Art
A leadless lead frame package (LLP) is an integrated circuit package design that contemplates the use of a lead frame in the formation of a chip scale package (CSP). The resulting packages are sometimes referred to as quad flat packs—no lead (QFN) packages. As illustrated in FIG. 1, in typical leadless lead frame packages, a copper lead frame strip or panel 101 is patterned (typically by stamping or etching) to define a plurality of arrays 103 of chip substrate features 105. Each chip substrate feature 105 includes a die attach pad 107 and a plurality of contacts 109 disposed about their associated die attach pad 107. Very fine tie bars 111 are often used to support the die attach pads 107 and contacts 109.
During assembly, dice are attached to the respective die attach pads and conventional wire bonding is used to electrically couple bond pads on each die to their associated contacts 109 on the lead frame strip 101. After the wire bonding, a plastic cap is molded over the top surface of the each array 103 of wire bonded dice. The dice are then singulated and tested using conventional sawing and testing techniques.
FIG. 2 illustrates a typical resulting leadless lead frame package. The die attach pad 107 supports a die 120 which is electrically connected to its associated contacts 109 by bonding wires 122. A plastic casing 125 encapsulates the die 120 and bonding wires 122 and fills the gaps between the die attach pad 107 and the contacts 109 thereby serving to hold the contacts in place. It should be appreciated that during singulation, the tie bars 111 are cut and therefore the only materials holding the contacts 109 in place is the molding material. The resulting packaged chip can then be surface mounted on a printed circuit board or other substrate using conventional techniques.
Since leadless lead frame packaging have proven to be a cost effective packaging arrangement, there are continuing efforts to provide further improvements to the package structure and/or processing to permit the package style to be used in additional applications and/or to improve specific characteristics of the resultant devices.